The ultraviolet spectrum generally is divided into three regions: UVA (400 nm-320 nm), UVB (320 nm-290 nm) and UVC (290 nm-200 nm). The UVA and UVB regions are important for suntan lamps and medical phototherapy applications and the UVC is important for germicidal lamp applications.
In recent years, there has been increasing interest in germicidal lamps because of concerns about supplying potable drinking water, especially during natural disasters. In addition, there is a concurrent interest worldwide in reducing the widespread use of mercury because of its environmental impact. These two factors taken together have led to the development of mercury-free (Hg-free) germicidal lamps. One such water disinfecting device described in U.S. Pat. No. 6,398,970 is a Xe-plasma based vacuum ultraviolet (VUV) excited lamp which is coated with phosphors emitting in the germicidal range of about 220-280 nm.
In addition to water purification, UVC-emitting phosphors may be used in other germicidal applications such as the purification of surfaces and air and the medical sterilization of open wounds. Other potential uses beyond germicidal applications include medical phototherapy and photo-curing of UV-sensitive polymers and resins. Also, the use of UVC-emitting phosphors in low-pressure mercury fluorescent lighting has been reported to improve light output and reduce degradation due to 185 nm radiation. See, e.g., U.S. Pat. No. 6,734,631.